The present invention relates to a display device and, more particularly, to the structure of a connecting part of a display device for connecting a flexible printed circuit board which inputs control signals to a display panel.
In a prior-art liquid crystal display device, a liquid crystal display panel includes, as shown in FIG. 6, a first substrate SUB1 and a second substrate SUB2 which are disposed to oppose each other via a liquid crystal layer, not shown. On the upper surface of the second substrate SUB2 disposed on the viewer's side, an upper polarization plate POL is attached. A lower polarization plate, not shown, is attached to the first substrate SUB1 disposed on the back side. On the surface on the liquid crystal layer side of the first substrate SUB1, such elements as pixel electrodes and thin-film transistors are formed. A drive circuit DR is mounted in an end portion of the first substrate SUB1. Also, a flexible printed circuit board FPC is electrically connected to the end portion of the first substrate SUB1. Control signals for image display are inputted from the flexible printed circuit board FPC to the drive circuit DR.
The flexible printed circuit board FPC includes a base film BF used as a base material and signal lines of metallic (e.g. copper) thin film are formed on a surface of the base film BF. The signal lines are covered with a cover layer of resin CV1 formed over the surface of the base film BF. The flexible printed circuit board FPC is electrically connected to the first substrate SUB1 via an anisotropic conductive film using connection terminals formed by laminating, for example, nickel (Ni) and gold (Au) over the signal line portions in an area (indicated by dashed-line ellipse B in FIG. 6) where the signal lines are exposed with the cover layer CV1 partly removed.
In a general flexible printed circuit board FPC, a portion, in an area along the end portion of the first substrate SUB1, of the cover layer CV1 is removed leaving the cover layer CV1 with a linear end portion. Therefore, when the flexible printed circuit board FPC is bent, bending points are generated to concentrate in an area along the linear end portion of the cover layer CV1 of the flexible printed circuit board FPC. This first causes the hard and brittle nickel (Ni) layer of the printed circuit board FPC to be broken, eventually causing signal lines to be broken.
As a means of solving the above problem, a liquid crystal display device has been disclosed in Japanese Patent Laid-Open No. H9 (1997)-138387 (Patent Document 1) and a corresponding U.S. Pat. No. 5,838,412 (Patent Document 2). The technique described in the above Patent Documents 1 and 2 is illustrated in FIG. 7 which is an enlarged view of where the flexible printed circuit board is connected to the first substrate SUB1 as seen in the direction of blank arrow P3 in FIG. 6. As shown in ellipse C in FIG. 7, the end portion of the cover layer CV1 is formed to be wavy including crests and troughs so that bending points generated when the flexible printed circuit board FPC is bent are distributed without being concentrated. This prevents the nickel (Ni) layer of the connection terminals and the signal lines formed on the flexible printed circuit board FPC from being broken.